The present invention relates to one-component alkoxy-functional RTV compositions, and more particularly, the present invention relates to scavengers for alkoxy-functional, one-component RTV compositions. The scavengers in such compositions result in the composition being shelf stable.
Early types of one-component RTV silicone rubber compositions are, for instance, disclosed in Ceyzeriat, U.S. Pat. No. 3,133,891, and Bruner, U.S. Pat. No. 3,035,016. Such patents disclose the use of acyloxy-functional silanes as cross-linking agents for such RTV compositions (RTV in this application refers to room temperature vulcanizable.) The compositions of Ceyzeriat were packaged in a substantially anhydrous state and when exposed to atmospheric moisture cured to a silicone elastomer. It was highly desirable to make such compositions as non-corrosive as possible, to be self-bonding, to be shelf stable and to have a fast cure rate. While the Ceyzeriat and Bruner compositions were shelf stable and fast-curing, nevertheless they had the disadvantage that they were somewhat corrosive and emit a somewhat pungent odor while curing.
It was highly desirable to make such compositions self-bonding, so that they would bond to most substrates without the use of a primer. This resulted in a saving on labor costs. Examples of disclosures which relate to increasing the adhesiveness or self-bonding properties of the Ceyzeriat composition are, for instance, disclosed in Kulpa, U.S. Pat. No. 2,961,161, Goossens, U.S. Pat. No. 3,296,195, and Beers, U.S. Pat. No. 3,428,930. A further example of acyloxy-functional RTV compositions can be, for instance, found in Beers, U.S. Pat. No. 4,257,932 and other related patents. However, even the composition of Beers, U.S. Pat. No. 4,257,932 which disclosed the use of a high carbon atom acyloxy-functional RTV, there resulted some discoloration of the metal on which the RTV was applied as a result of the fact that the composition released a high molecular weight acid when it cured (2-ethylhexanoic acid).
Accordingly, it was highly desirable to make a one-component, non-corrosive RTV composition, comparable in shelf stability and curing properties to the Bruner and Ceyzeriat corrosive acyloxy-functional, one-component RTV systems. It was early known that two-component RTV compositions were noncorrosive since they relied on a cross-linking agent which released an alcohol upon curing. An example of a two-component RTV composition is, for instance, to be found in Nitzsche et al., U.S. Pat. No. 3,127,363. The only trouble with the Nitzsche et al. composition was that it was two-component and required the additional labor step of taking the packages and mixing them together in the appropriate ratios and then quickly applying the composition to whatever form was desired in which it was to be cured. The composition had to be applied in a rapid manner since it had a very poor shelf life once it was mixed. Accordingly, such compositions were not altogether desirable.
It was desired to make such compositions one-component because of the noncorrosive characteristics. Accordingly, an early disclosure of a one-component alkoxy-functional RTV system is to be found in Nitzsche et al., U.S. Pat. No. 3,065,194. The difficulty with the Nitzsche et al., U.S. Pat. No. 3,065,194 composition was that the composition had to be vigorously dried during preparation and had a very short shelf life. Early one-component alkoxy-curing systems are to be found in Brown et al., U.S. Pat. No. 3,122,522, Brown et al., U.S. Pat. No. 3,161,614 or U.S. Pat. No. RE-29760, which disclosed polyalkoxy-terminated polymers. The difficulty with these polymers was that they did not cure at a sufficient rate, that is they were not fast-curing, and furthermore if they cured at all, had a very poor shelf life.
It should be noted that the term "shelf life" in this application means that the composition, after it has been stored for periods of one month to one year after manufacture, will cure at about the same rate and to about the same degree of final cure as the composition that is cured immediately or a few days after manufacture.
Accordingly, it was highly desirable to make such compositions shelf stable and be fast-curing. Examples of noncorrosive, one-component alkoxy-functional RTV systems which, in some cases, were commercialized are disclosed by Weyenberg, U.S. Pat. No. 3,334,067, Cooper et al., U.S. Pat. No. 3,542,901 and by Smith et al., U.S. Pat. Nos. 3,689,454 and 3,779,986. These applications relied on the particular use of specific titanium chelate catalysts in place of a tin soap condensation catalyst to accelerate the cure of the composition. As stated previously, although some of the compositions disclosed in the above patents were commercialized, nevertheless, the compositions still did not have a sufficiently fast cure rate even with the specialized chelate catalysts and even then did not have a sufficient shelf life. A specific type of alkoxy-functional, one-component RTV system which has been commercialized and has a number of advantages in terms of noncorrosiveness and low modulus properties is to be found, for instance, in the disclosure of Beers, U.S. Pat. No. 4,100,129 which is hereby incorporated by reference. The composition of this patent is noncorrosive, is low modulus and has self-bonding properties in view of the self-bonding additives incorporated into the composition. However, even the composition of this patent was not sufficiently fast-curing and did not have a sufficient shelf life, that is, after a period of six months, one year or more, the shelf life of the composition was poor. Examples of adhesion promoters that could be utilized with such a composition are, for instance, to be found disclosed in Mitchell et al., U.S. Pat. No. 4,273,698 which is hereby incorporated by reference. All the patents referred to in this application are incorporated by reference into the present case. However good the self-bonding properties of the Beers composition are, it nevertheless still suffered from not having as good a shelf life as would be desired and not being as fast curing as would be desired. Accordingly, it was highly desirable to find a noncorrosive self-bonding RTV composition which was low modulus and was shelf stable and fast-curing.
The above RTV systems that have been disclosed are alkoxy-functional and acyloxy-functional. There are also other types of functional one-component RTV systems. An example of an amine-functional RTV system is, for instance, to be found in disclosures of the following U.S. patents: Nitzsche et al., U.S. Pat. No. 3,032,528; Hittmair et al., U.S. Pat. No. 3,408,325; Nitzsche et al., U.S. Pat. No. 3,923,736; Hittmair et al., U.S. Pat. No. 3,464,951.
There are also disclosed in various patents one-component amide-functional RTV systems, aminoxy-functional RTV systems, ketoxime-functional RTV systems, etc. Recently, there has been developed a one-component alkoxy-functional RTV system which is shelf stable and fast curing as disclosed in White et al., Ser. No. 277,524 filed on June 26, 1981. A companion disclosure to that case is Halgren, Ser. No. 277,525 which was filed on June 26, 1981 and is also incorporated relevant.
Basically, the White et al. docket discloses the production of a shelf-stable, fast-curing, one-component alkoxy-functional RTV system which is cured with a tin compound by having a scavenger in this system. The scavenger, which can be either a separate compound or part of the alkoxy-functional cross-linking agent, operates by absorbing all unbonded or free hydroxy groups in the RTV mixture so as to prevent the hydroxy groups from degrading and cross-linking the polymer mixture, thus deleteriously affecting its shelf life and curing properties. It is disclosed in this patent application that the scavenger may be amine-functional, that is, either the separate scavenger compound may be amine-functional or the combined cross-linking agent scavenger may be amine-functional. There is further disclosed that amine-functional accelerators may be utilized in the composition especially when the scavenger is enoxy-functional. Although certain simple types of amines are disclosed in this application, there is nowhere disclosed the utilization of silazanes and silyl-nitrogen polymers. The difficulty with the amine scavenger as disclosed in the White et al. Ser. No. 277,524 is that while they are known, nevertheless they have to be specially prepared for the composition of White. On the other hand, silazanes like hexamethyldisilazane are readily available in any silicone manufacturing plant. More importantly, however, the amines of White et al. Ser. No. 277,524, give a noticeable odor to the composition while on the other hand, hexamethyldisilazane imparts to the RTV composition a slight odor of ammonia.
Be that as it may, there are other silyl-nitrogen compounds that can be utilized as scavengers for the compositions of Ser. No. 277,524 other than ones disclosed in White et al. Ser. No. 277,524 which is the object of the present case. Other improvements over White et al. Ser. No. 277,524 are, for instance, to be found in Chung, Ser. No. 338,518 filed on Jan. 11, 1982 and Lucas, et al., Ser. No. 349,538, filed on the same date as the present case and entitled, Adhesion Promoters for One-Component RTV Silicone Compositions, and Beers, Ser. No. 349,537 entitled Low Modulus One-Component RTV Compositions and Processes also filed on the same date as the present case. The Lucas et al. case discloses various adhesion promoters for the compositions of White et al. Ser. No. 277,524 while Ser. No. 349,537 discloses various types of additives that can be added to the compositions of White et al. Ser. No. 277,524 to make the composition low modulus.
The disclosure of Chung Ser. No. 338,518 deals with various types of other scavengers that may be utilized with the White et al. composition as does the present case.
Accordingly, it is one object of the present invention to provide for a noncorrosive, alkoxy-functional, one-component RTV system that is shelf stable and fast-curing.
It is an additional object of the present invention to provide for silyl-nitrogen scavengers for alkoxy-functional, one-component RTV systems so as to make them shelf stable and fast curing.
It is yet an additional object of the present invention to provide silyl-nitrogen scavengers for alkoxy-functional, one-component RTV systems such that the compositions do not have an objectionable odor.
It is still an additional object of the present invention to provide for a noncorrosive, alkoxy-functional, one-component RTV system that is relatively inexpensive to produce.
It is a further object of the present invention to provide a process for producing a relatively inexpensive noncorrosive, one-component RTV composition which is shelf stable and fast curing and which does not have an objectionable odor.
This and other objects of the present invention are accomplished by means of the disclosures set forth herein and below.